Taoiseach Enda Kenny confirmed the boat will be built to the exact dimensions of the recently commissioned LE Samuel Beckett and the second vessel being added to the fleet, the LE James Joyce, which is still being built.

"I recently attended the commissioning ceremony of LE Samuel Beckett, which brought home to me the necessity to continue with the vessel replacement strategy," Mr Kenny said.

"The new ship is impressive and offers excellent value and I am convinced that this is the right time to maintain the momentum with the replacement strategy and move forward with a placing of a contract for the third patrol vessel."

Babcock Marine, which built the first two replacement vessels for the navy, has been selected to supply the third at 2012 prices - an option that was secured under the existing contract.

The near 90m long OPV90 class ships are 12m longer than their predecessors, which were decommissioned after 30 years on the seas.

The Devon boat builders use sleek designs by STX Marine with improved sea-keeping qualities which provide for better working conditions at sea and bigger aft-deck space provides for storage of containers for potential UN missions requiring humanitarian supplies and equipment.

The ships can reach maximum speeds of 23 knots and have a range of 6,000 nautical miles. They are also fitted with a 76mm gun mounted at the bow.

Mr Kenny, who assumed responsibility for the Department of Defence following the resignation of Alan Shatter last month, said the third vessel will be delivered in 2016.

"The Naval Service carries out a wide range of challenging roles. Naval Service ships assert the integrity of our territorial waters as well as protecting the marine resources of the country. The Naval Service's operational capacity in a highly demanding environment will be enhanced when the three new offshore vessels are in service," he said.

The department said the option to go with Babcock Marine for the third vessel ensures the fleet is standardised and the upgrade can be completed in the next two years rather than waiting another five years for the final ship.